Control systems are used in a variety of applications. In simple configurations, these systems can include proportional-integral (PI), and proportional-integral-derivative (PID) controllers. These controllers can be implemented in mechanical, analog electronic, or digital electronic forms. Mechanical control systems are usually limited to relatively simple mechanical systems. Therefore, for controlling systems involving electrical sensors or actuators, particularly in aerospace applications, electronic controllers are typically employed.
Analog electronic systems can be designed that feature relatively fast response times. However, analog systems are typically inflexible, and can suffer from performance variations due to changes in ambient conditions, age, or other variables. For complex control systems, digital controllers are increasingly popular. Digital implementations can include the use of general purpose processors executing software instructions, application specific digital signal processors (DSPs) or integrated circuits, or field programmable gate arrays.
General purpose space flight qualified microprocessors with floating point co-processors provide floating point processing capability, but at a much slower processing speed and generally do not provide additional interfaces to A/D and D/A devices. These devices also require project specific software in order to implement the Controls System algorithm. Commercial microcontroller digital signal processor application-specific chipsets have been used for non-space flight applications. General purpose space flight qualified microprocessors with floating point co-processors combined with application specific field programmable gate arrays (FPGAs) have been used for space flight applications. However, the flexibility and scalability of such systems has been limited. Commercial Microcontroller DSP application-specific chipsets provide the technical features (floating point processing capability with standard serial peripheral interface bus (SPI) interfaces to analog to digital (A/D), (D/A) devices), but cannot survive the space environment.